"It is absolutely essential for each user to have UID that doesn't change and is consistent for the life of the account." I agree and that's actually been a pr

"It is absolutely essential for each user to have UID that doesn't change and is consistent for the life of the account." I agree and that's actually been a problem with Twitter. They do have a unique ID for each user. The problem resides in the fact that users can change their Twitter handles. So you can track a user with their UID, but you also have to check that their handle doesn't change over time and figure out if their user page on your site is at website.com/223453245/ (not the prettiest and people can't link the Twitter handle to the user page on your site), or website.com/handle/ (which is more desirable but creates problems when the handle changes).